I am trying to use global optimization to solve a problem, but get an error:
 

> GlobalOptimization:-GlobalSolve(R, {eq}, h = 50 .. 10000, R = 50 .. 10000, maximize);

Error, `GlobalOptimization` does not evaluate to a module

What is meant by this error?

eqn := (A/(1+a*exp(-b*(((atan(h/R))*(180/Pi))-a)))) +10*log10(h^2+R^2)+20*log10(f)+20*log10(4*Pi/c)+nNLOS = 110;

R and h are my unknown variables in the equation

The rest of variables, A,c,f,a,b,NLOS are known.

I need to find solution such that derivate of R w.r.t h = 0, I want to maximize R.
But this equation is implicit, R cannot be separated on one side of the equation. I tried:

> implicitdiff(eq, R, h);

But I get the error:

Warning, solutions may have been lost